A person’s height is associated with increased risk for venous thromboembolism (VTE) according to a study published in the American Heart Association journal, Circulation: Cardiovascular Genetics. In the study, ‘Body Height and Incident Risk of Venous Thromboembolism - A Cosibling Design’, of more than two million Swedish siblings, researchers found that the risk of venous thromboembolism was associated with height, with the lowest risk being in shorter participants.

"Height is not something we can do anything about," said lead researcher, Dr Bengt Zöller, associate professor at Lund University and Malmö University Hospital in Malmö, Sweden. "However, the height in the population has increased, and continues increasing, which could be contributing to the fact that the incidence of thrombosis has increased."

The CDC estimates venous thromboembolism affects up to 600,000 Americans every year, making it the third leading cause of heart attack and stroke. The most common triggers are surgery, cancer, immobilization and hospitalization. In women, pregnancy and use of hormones like oral contraceptive or oestrogen for menopause symptoms are also important triggers.

Although body height has been associated with an increased risk of VTE, the study authors said that the association can be confounded with shared familial factors (genetic/environmental). Therefore, the used a co-sibling design to further their understanding the relationship between VTE and height.

Using Swedish national registry databases, they used a co-relative design with full siblings alongside a general Swedish population sample. A cohort of male conscripts (n=1,610870), born in 1951 to 1992 without previous VTE, was followed from enlistment (1969–2010) until 2012. Another cohort of first-time pregnant women (n=1,093342) from the medical birth register, without previous VTE, was followed from first pregnancy (1982–2012) until 2012. Using the Multi-Generation Register, they identified all full-sibling pairs discordant for height. This co-sibling design allowed for adjustment for familial factors (genetic/environmental).

Compared with the tallest women (>185cm) and men (>190cm), there was a graded decreased risk by lower height for both men and women. The risk was lowest in women and men with the shortest stature (<155 and <160cm, respectively): hazard ratios=0.31 (95% confidence interval, 0.22–0.42) and 0.35 (95% confidence interval, 0.22–0.55), respectively.

There was a graded association also in the co-sibling design comparing siblings with varying degree of discordance for height (reference was the taller sibling): ≥10cm difference between brothers hazard ratios=0.69 (95% confidence interval, 0.61–0.78) and sisters hazard ratios=0.65 (95% confidence interval, 0.52–0.80), respectively.

Zöller said gravity may influence the association between height and venous thromboembolism risk. "It could just be that because taller individuals have longer leg veins there is more surface area where problems can occur," said Zöller. "There is also more gravitational pressure in leg veins of taller persons that can increase the risk of blood flow slowing or temporarily stopping."

One caution is that researchers didn't have access to data for childhood and parent lifestyle factors such as smoking, diet and physical activity. In addition, the study consisted primarily of Swedish people and may not be translatable to the US population. Although, researchers note, the Swedish population nowadays is as ethnically diverse as the US population.

"I think we should start to include height in risk assessment just as overweight, although formal studies are needed to determine exactly how height interacts with inherited blood disorders and other conditions," added Zöller.